Development of Novel Mouse Monoclonal Antibodies against Human CD19

CD19 is a type I transmembrane glycoprotein belonging to the immunoglobulin superfamily. It is expressed in normal and neoplastic B cells, and it modulates the threshold of B cell activation for amplifying B cell receptor signaling. Blinatumomab (a CD3-CD19-bispecific T cell-engaging antibody) and tisagenlecleucel (genetically modified T cells that express a CD19 chimeric antigen receptor [CART-19]) provide significant benefits for patients with CD19-positive relapsed or refractory B cell malignancies. In this study, we first employed the Cell-Based Immunization and Screening (CBIS) method to produce anti-CD19 monoclonal antibodies using CD19-overexpressing cells for both immunization and screening. One established clone - C₁₉Mab-1 - proved to be useful in flow cytometry assays against lymphoma cell lines, such as BALL-1, P30/OHK, and Raji. Second, the extracellular domain of CD19 was immunized into mice, and enzyme-linked immunosorbent assays were performed for the first screening. One established clone - C₁₉Mab-3 - was determined to be useful for Western blotting and immunohistochemical analysis. Due to their complementary utility, a combination of C₁₉Mab-1 (established using CBIS) and C₁₉Mab-3 (established using conventional method) could be useful for the pathological analysis of CD19.